Answer:
[tex]\dfrac{1}{64}[/tex]
Step-by-step explanation:
Hemi-, demi- and semi- are prefixes which mean half.
When applied to musical notation, each time a prefix is added it means the note's value is halved.
Therefore, if a quaver is one-eighth of a semibreve, then a semiquaver is half of a quaver, which means it's one-sixteenth of a semibreve.
[tex]\large \begin{aligned}\sf quaver & = \sf\dfrac{1}{8}\:of\:a\:semibreve\\\\\implies \sf hemisemidemiquaver & = \sf \dfrac{1}{2} \times \dfrac{1}{2} \times \dfrac{1}{2} \times quaver\\\\& = \sf \dfrac{1}{2} \times \dfrac{1}{2} \times \dfrac{1}{2} \times \dfrac{1}{8}\\\\& = \sf \dfrac{1}{64}\:of\:a\:semibreve\end{aligned}[/tex]
Therefore, a hemisemidemiquaver is one-sixty-fourth of a semibreve.
